Large-scale mainframe computers continue to be used extensively across many industries. Historically, tape storage has been used to provide permanent and temporary data protection services to those mainframes. In such environments, it is not uncommon for mainframe tape libraries to hold hundreds of TeraBytes (TB) of data spread across tens of thousands of tape volumes.
Virtual tape emulation (VTE) products such as data library for mainframe (DLm) available from EMC Corporation of Hopkinton, Mass. can be used to emulate a given number of tape volumes to the mainframe using disk drives as the storage media instead of magnetic tape. As a mainframe-based application writes data to what it believes is a tape drive, that data is actually stored as a tape volume image on direct access storage device such as a disk array subsystem system. Each individual tape volume written by the mainframe becomes a single disk file on the file system on the disk array.
Such VTE products ultimately allow the operators of mainframe data centers to move from a tape-based backup solution to a disk-based backup solution, leveraging today's high speed low cost disk technology to provide an innovative approach to data storage.
The mainframe host writes data to the virtual tape drive using the same commands as it would as if it were writing to an actual magnetic tape drive. These commands include “mount requests”, which are actions that would require a physical tape storing recorded data to be mounted onto a tape drive in a physical tape server system. The mount requests processed by the VTEs can include read and write requests. When data volumes are written to or read from the network storage devices, the virtual tape file system is “mounted” by the VTE.
For a write mount request, a VTE can process an arriving mainframe tape volume and write it as a single file on the disk library for mainframe storage. Each mainframe tape can be stored as a single file having a file name can be the tape volume serial number (VOLSER). The file only consumes as much space as required to store the file resulting in no wasted storage space.
VTEs can be enhanced file system (EFS) VTEs or non-EFS VTEs. A difference between EFS VTEs and non-EFS VTEs is the named volume format. For non-EFS VTEs, volume names in a file system are designated by the first two letters of the tape volume serial number (VOLSER). For example, when a named mount for VOLSER AB1234 is requested, the file system, “/tapelib/AB” which matches the first two letters of the file name. In contrast, on EFS VTEs, there are no requirements that the first two letters of the named volumes designate a specific file system. Thus, a volume having a VOLSER AB1234 can be stored in any file system. When a named mount is requested, the EFS VTE may have to search every file system in order to find the requested VOLSER which can be very time consuming. Thus, a byproduct of the EFS feature is a mount delay which can slow named mount request processing. What is needed is a improved method for system and method for optimizing named mounts on EFS enabled VTEs.